%0 Journal Article
%A Rohe, Tim
%A Noppeney, Uta
%T Reliability-Weighted Integration of Audiovisual Signals Can Be Modulated by Top-down Control
%D 2018
%R 10.1523/ENEURO.0315-17.2018
%J eneuro
%P ENEURO.0315-17.2018
%X Behaviorally, it is well-established that human observers integrate signals near-optimally weighted in proportion to their reliabilities as predicted by maximum likelihood estimation. Yet, despite abundant behavioral evidence, it is unclear how the human brain accomplishes this feat. In a spatial ventriloquist paradigm, participants were presented with auditory, visual and audiovisual signals and reported the location of the auditory or the visual signal. Combining psychophysics, multivariate fMRI decoding and models of maximum likelihood estimation (MLE), we characterized the computational operations underlying audiovisual integration at distinct cortical levels. We estimated observers’ behavioral weights by fitting psychometric functions to participants’ localization responses. Likewise, we estimated the neural weights by fitting ‘neurometric’ functions to spatial locations decoded from regional fMRI activation patterns. Our results demonstrate that low-level auditory and visual areas encode predominantly the spatial location of the signal component of a region’s preferred auditory (resp. visual) modality. By contrast, intraparietal sulcus forms spatial representations by integrating auditory and visual signals weighted by their reliabilities. Critically, the neural and behavioral weights and the variance of the spatial representations depended not only on the sensory reliabilities as predicted by the MLE model but also on participants’ modality-specific attention and report (i.e., visual vs. auditory). These results suggest that audiovisual integration is not exclusively determined by bottom-up sensory reliabilities. Instead, modality-specific attention and report can flexibly modulate how intraparietal sulcus integrates sensory signals into spatial representations to guide behavioral responses (e.g., localization and orienting).Significance Statement To obtain an accurate representation of the environment, the brain should integrate noisy sensory signals by weighting them in proportion to their relative reliabilities. This strategy is optimal by providing the most reliable, i.e., least variable percept. The extent to which the brain top-down controls the sensory weights in the integration process remains controversial. The current study shows that the parietal cortex weighs audiovisual signals by their reliabilities. Yet, the sensory weights and the variance of the multisensory representations were also influenced by modality-specific attention and report. These results suggest that audiovisual integration can be flexibly modulated by top-down control.
%U http://www.eneuro.org/content/eneuro/early/2018/02/16/ENEURO.0315-17.2018.full.pdf